Immunoassays and similar diagnostic procedures are of major importance in health care and clinical research. Many clinical laboratories perform a large number of such procedures on a routine basis, which involves the handling of a multitude of samples, reagents, and microtiter wells and a large number of repetitions of steps and procedures. The development of automated analyzers has reduced the opportunities for human error and improved the efficiency, accuracy and reliability of these procedures, with consequential reductions in cost. One example of an automated analyzer of this type is the analyzer disclosed in co-pending, commonly owned U.S. patent application Ser. No. 07/732,858, filed Jul. 19, 1991, entitled "Automated Clinical Analyzer," Christopher J. Macko, Donald R. Flory and Jordan S. Honig, inventors. An additional application of potential interest for its disclosure of related equipment is co-pending, commonly owned U.S. patent application Ser. No. 07/732,861, filed Jul. 19, 1991, entitled "Rack-Suspendable Carrier for Clinical Assay Wells With Removable Lid," Jordan S. Honig, inventor. Both such applications are incorporated herein by reference.
The analyzer disclosed in Ser. No. 07/732,858 and others of similar function use various types of assay reagents arranged in combinations, each combination containing the reagents required for a single assay, with sufficient quantities of each reagent so that the assay can be performed on a multitude of samples. Since the reagents are held in troughs or other receptacles from which aliquots are drawn by automated pipets, such arrangements raise a number of concerns. One concern is the exposure of the reagents to the environment during the periods of time between aliquot withdrawals. Certain reagents are susceptible to chemical change when left in open containers. Another concern is the evaporation of solvents from the reagents. This causes an increase in the reagent concentration, which is not compensated for by the automated pipetting. The result is a loss of accuracy and reproducibility in the assay results.